U.S. patent application number 11/548009 was filed with the patent office on 2008-04-10 for method of forming lithographic and sub-lithographic dimensioned structures.
Invention is credited to Toshiharu Furukawa, David Vaclav Horak, Charles William Koburger.
Application Number | 20080085600 11/548009 |
Document ID | / |
Family ID | 39275275 |
Filed Date | 2008-04-10 |
United States Patent
Application |
20080085600 |
Kind Code |
A1 |
Furukawa; Toshiharu ; et
al. |
April 10, 2008 |
METHOD OF FORMING LITHOGRAPHIC AND SUB-LITHOGRAPHIC DIMENSIONED
STRUCTURES
Abstract
A method of forming lithographic and sub-lithographic
dimensioned structures. The method includes forming a mandrel layer
on a top surface of an underlying layer and then forming a masking
layer on a top surface of the mandrel layer; patterning the masking
layer into a pattern of islands; transferring the pattern of
islands into the mandrel layer to form mandrel islands, the top
surface of the underlying layer exposed in spaces between the
mandrel islands; forming first spacers on sidewalls of the mandrel
islands; removing the mandrel islands, the top surface of the
underlying layer exposed in spaces between the first spacers;
forming second spacers on sidewalls of the first spacers; and
removing the first spacers, the top surface of the underlying layer
exposed in spaces between the second spacers.
Inventors: |
Furukawa; Toshiharu; (Essex
Junction, VT) ; Horak; David Vaclav; (Essex Junction,
VT) ; Koburger; Charles William; (Delmar,
NY) |
Correspondence
Address: |
SCHMEISER, OLSEN & WATTS
22 CENTURY HILL DRIVE, SUITE 302
LATHAM
NY
12110
US
|
Family ID: |
39275275 |
Appl. No.: |
11/548009 |
Filed: |
October 10, 2006 |
Current U.S.
Class: |
438/637 ;
257/E21.038; 257/E21.039; 257/E21.257 |
Current CPC
Class: |
H01L 21/76816 20130101;
H01L 21/0338 20130101; H01L 21/0337 20130101; H01L 21/31144
20130101 |
Class at
Publication: |
438/637 |
International
Class: |
H01L 21/4763 20060101
H01L021/4763 |
Claims
1. A method, comprising: forming a mandrel layer on a top surface
of an underlying layer and then forming a masking layer on a top
surface of said mandrel layer; patterning said masking layer into a
pattern of islands; transferring said pattern of islands into said
mandrel layer to form mandrel islands, said top surface of said
underlying layer exposed in spaces between said mandrel islands;
forming first spacers on sidewalls of said mandrel islands;
removing said mandrel islands, said top surface of said underlying
layer exposed in spaces between said first spacers; forming second
spacers on sidewalls of said first spacers; and removing said first
spacers, said top surface of said underlying layer exposed in
spaces between said second spacers.
2. The method of claim 1, further including: prior to said
transferring, reducing dimensions of said islands in directions
parallel to said top surface of said underlying layer.
3. The method of claim 2, wherein said patterning includes
performing a photolithographic process and said dimensions, after
reduction, are less than a minimum dimension of a line/space
printable by said photolithographic process.
4. The method of claim 1, further including, etching trenches into
said underlying layer in regions of said underlying layer not
protected by said second spacers.
5. The method of claim 4, wherein said patterning includes
performing a photolithographic process and at least one dimension
of at least one of said trenches in a direction parallel to said
top surface of said underlying layer being less than a minimum
dimension of a line/space printable by said photolithographic
process.
6. The method of claim 4, wherein said undying layer comprises
dielectric material and said method further includes removing said
second spacers and filling said trenches with an electrically
conductive material.
7. The method of claim 4, further including: prior to said etching,
forming an additional masking layer on additional regions of said
underlying layer, said additional masking layer preventing etching
of said underlying layer in said additional regions.
8. The method of claim 1, further including: after said removing
said first spacers, forming an additional masking layer on a top
surface of said underlying layer and on said second spacers;
patterning said additional masking layer into a pattern of
additional islands, selected regions of said additional islands
overlapping selected regions of said second spacers, first regions
of said underlying layer exposed between said second spacers, and
second regions of said underlying layer exposed in spaces between
said additional islands.
9. The method of claim 8, further including, etching first trenches
into said underlying layer in said first regions of said underlying
layer not protected by said second spacers and etching second
trenches into said second regions of said underlying layer not
protected by said additional islands.
10. The method of claim 8, wherein said patterning of said masking
layer includes performing a first photolithographic process and
said patterning of said additional masking layer includes
performing a second photolithographic process, at least one
dimension of at least one of said first trenches in a direction
parallel to said top surface of said underlying layer being less
than a minimum dimension of a line/space printable by said first
photolithographic process and all dimensions of said second
trenches in directions parallel to said top surface of said
underlying layer being equal to greater than said minimum dimension
of said line/space printable by said first photolithographic
process.
11. The method of claim 8, wherein said underlying layer comprises
dielectric material and further including removing said second
spacers and said additional islands and filling said first and
second trenches with an electrically conductive material.
12. A method comprising: forming one or more mandrel islands on a
top surface of an underlying layer; forming first spacers on
sidewalls of said one or more mandrel islands and then removing
said one or more mandrel islands, said first spacers defining a
first pattern; forming second spacers on sidewalls of said first
spacers and then removing said first spacers, said second spacers
defining a second pattern, said second pattern a reverse of said
first pattern where said second spacers had completely covered said
underlying layer between adjacent first spacers; and etching
trenches into said underlying layer in regions of said underlying
layer where said underlying layer is not protected by said second
spacers.
13. The method of claim 12, further including: filling said
trenches with a fill material.
14. The method of claim 13, wherein said underlying layer comprises
dielectric material and said fill material is electrically
conductive.
15. The method of claim 12, wherein said one or more mandrel
islands are formed using a photolithographic process and at least
one dimension of at least one of said trenches in a direction
parallel to said top surface of said underlying layer is less than
a minimum dimension of a line/space printable by said
photolithographic process.
16. The method of claim 12, further including: performing a first
photolithographic process to form said mandrel islands; between
said removing said first spacers and said etching, performing a
second photolithographic process, said second photolithographic
process forming protective islands, selected regions of said
protective islands overlapping selected regions of said second
spacers, additional regions of said underlying layer exposed in
spaces between said protective islands; and simultaneously with
said etching trenches, etching additional trenches in regions of
said underlying layer exposed between said protective islands, at
least one dimension of at least one of said trenches in a direction
parallel to said top surface of said underlying layer being less
than a minimum dimension of a line/space printable by said first
photolithographic process and all dimensions of said additional
trenches in directions parallel to said top surface of said
underlying layer being equal to or greater than said minimum
dimension of said line/space printable by said first
photolithographic process.
17. A method comprising: forming a dielectric mandrel layer on a
top surface of an underlying layer and then forming a first
photoresist layer on a top surface of said mandrel layer;
performing a first photolithographic process to form said first
photoresist layer into a pattern of first photoresist regions;
transferring said pattern of first photoresist regions into said
mandrel layer to form mandrel islands, said top surface of said
underlying layer exposed in spaces between said mandrel islands;
removing said first photoresist regions; forming first spacers on
sidewalls of said mandrel islands; removing said mandrel islands,
said top surface of said underlying layer exposed in spaces between
said first spacers; forming second spacers on sidewalls of said
first spacers; removing said first spacers, said top surface of
said underlying layer exposed in spaces between said second
spacers; forming a second photoresist layer on said top surface of
said mandrel layer; and performing a second photolithographic
process to form said second photoresist layer into a pattern of
second photoresist regions, selected regions of said second
photoresist regions overlapping selected regions of said second
spacers, first regions of said underlying layer exposed between
said second spacers, and second regions of said underlying layer
exposed in spaces between said second photoresist regions.
18. The method of claim 17, further including: prior to said
transferring, reducing dimensions of said first photoresist regions
in directions parallel to said top surface of said underlying
layer, at least one dimension of at least one of said photoresist
regions being less than a minimum dimension of a line/space
printable by said first photolithographic process.
19. The method of claim 17, further including: etching first
trenches into said underlying layer in said first regions of said
underlying layer not protected by said second spacers, at least one
dimension of at least one of said trenches in a direction parallel
to said top surface of said underlying layer being less than a
minimum dimension of a line/space printable by said first
photolithographic process; and etching second trenches into said
second regions of said underlying layer not protected by said
second photoresist regions, and all dimensions of said second
trenches in directions parallel to said top surface of said
underlying layer being equal to greater than said minimum dimension
of said line/space printable by said first photolithographic
process.
20. The method of claim 19, further including: filling said first
and second trenches with an electrical conductor comprising copper,
tungsten, tantalum, tantalum nitride, titanium, titanium nitride,
aluminum or combinations thereof, and wherein said underlying layer
comprises hydrogen silsesquioxane polymer, methyl silsesquioxane
polymer, polyphenylene oligomer, methyl doped silica,
organosilicate glass, porous organosilicate glass, silicon dioxide,
silicon nitride, silicon carbide, silicon oxy nitride, silicon oxy
carbide, organosilicate glass, plasma-enhanced silicon nitride or
NBLok.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of integrated
circuit fabrication; more specifically, it relates to a method for
forming lithographic and sub-lithographic structures.
BACKGROUND OF THE INVENTION
[0002] As the performance of integrated circuits has increased and
size of integrated circuits has decreased, the sizes of the
structures making up the integrated circuit have also decreased.
These structures are defined lithographically and there is a
minimum feature size that can be defined by lithographic processes.
While lithographic technology has and continues to reduce this
minimum feature size by employing shorter wavelength exposure
radiation and increasing effective numerical aperture, the pace of
this reduction in minimum feature size has begun to slow. At the
same time, while some structures impart a benefit to integrated
circuits the smaller they get, other structures do not. Also, for
some structures, it is better that they have dimensions less than
the lithographic minimum feature size. Therefore, there is a need
for a method for forming structures having lithographic and
sub-lithographic dimensions.
SUMMARY OF THE INVENTION
[0003] A first aspect of the present invention is a method,
comprising: forming a mandrel layer on a top surface of an
underlying layer and then forming a masking layer on a top surface
of the mandrel layer; patterning the masking layer into a pattern
of islands;
[0004] transferring the pattern of islands into the mandrel layer
to form mandrel islands, the top surface of the underlying layer
exposed in spaces between the mandrel islands; forming first
spacers on sidewalls of the mandrel islands; removing the mandrel
islands, the top surface of the underlying layer exposed in spaces
between the first spacers; forming second spacers on sidewalls of
the first spacers; and removing the first spacers, the top surface
of the underlying layer exposed in spaces between the second
spacers.
[0005] A second aspect of the present invention is a method
comprising: forming one or more mandrel islands on a top surface of
an underlying layer; forming first spacers on sidewalls of the one
or more mandrel islands and then removing the one or more mandrel
islands, the spacers defining a first pattern; forming second
spacers on sidewalls of the first spacers and then removing the
first spacers, the second spacers defining a second pattern, the
second pattern a reverse of the first pattern where the second
spacers had completely covered the underlying layer between
adjacent first spacers; and etching trenches into the underlying
layer in regions of the underlying layer where the underlying layer
is not protected by the second spacers.
[0006] A third aspect of the present invention is a method
comprising: forming a mandrel layer on a top surface of an
underlying layer and then forming a first photoresist layer on a
top surface of the mandrel layer; performing a first
photolithographic process to form the first photoresist layer into
a pattern of first photoresist regions; transferring the pattern of
first photoresist regions into the mandrel layer to form mandrel
islands, the top surface of the underlying layer exposed in spaces
between the mandrel islands; removing the first photoresist
regions; forming first spacers on sidewalls of the mandrel islands;
removing the mandrel islands, the top surface of the underlying
layer exposed in spaces between the first spacers; forming second
spacers on sidewalls of the first spacers; removing the first
spacers, the top surface of the underlying layer exposed in spaces
between the second spacers; forming a second photoresist layer on
the top surface of the second spacers; and performing a second
photolithographic process to form the second photoresist layer into
a pattern of second photoresist regions, selected regions of the
second photoresist regions overlapping selected regions of the
second spacers, first regions of the underlying layer exposed
between the second spacers, and second regions of the underlying
layer exposed in spaces between the second photoresist regions.
BRIEF DESCRIPTION OF DRAWINGS
[0007] The features of the invention are set forth in the appended
claims. The invention itself, however, will be best understood by
reference to the following detailed description of an illustrative
embodiment when read in conjunction with the accompanying drawings,
wherein:
[0008] FIGS. 1A, 2A, 3A, 4A, 5A, 6A, 7A, 8A, 9A and 10A are top
views, FIGS. 1B, 2B, 3B, 4B, 5B, 6B, 7B, 8B, 9B and 10B are
cross-sectional views through respective lines 1B-1B, 2B-2B, 3B-3B,
4B-4B, 5B-5B, 6B-6B, 7B-7B, 8B-8B, 9B-9B and 10B-10B of respective
FIGS. 1A, 2A, 3A, 4A, 5A, 6A, 7A, 8A, 9A and 10A and FIGS. 8C and
9C are cross-sectional views through respective lines 8C-8C and
9C-9C of respective FIGS. 8A and 9A illustrating steps in the
fabrication of a structure according to embodiments of the present
invention; and
[0009] FIG. 11A is a top view and FIG. 11B is a cross-sectional
view through line 11B-11B of FIG. 11A illustrating a further step
in the fabrication of a structure according to embodiments of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0010] FIGS. 1A, 2A, 3A, 4A, 5A, 6A, 7A, 8A, 9A and 10A are a top
views, FIGS. 1B, 2B, 3B, 4B, 5B, 6B, 7B, 8B, 9B and 10B are
cross-sectional views through respective lines 1B-1B, 2B-2B, 3B-3B,
4B-4B, 5B-5B, 6B-6B, 7B-7B, 8B-8B, 9B-9B and 10B-10B of respective
FIGS. 1A, 2A, 3A, 4A, 5A, 6A, 7A, 8A, 9A and 10A and FIGS. 8C and
9C are cross-sectional views through respective lines 8C-8C and
9C-9C of respective FIGS. 8A and 9A illustrating steps in the
fabrication of a structure according to embodiments of the present
invention.
[0011] In FIGS. 1A and 1B, formed on a top surface of an underlying
layer 100 is a mandrel layer 105. In one example underlying layer
100 is an interlevel dielectric layer (ILD) which itself is formed
on a semiconductor substrate (not shown). Formed on a top surface
of mandrel layer 105 are photoresist regions 110A and 110B.
Photoresist regions 110A and 110B are formed by applying a
photoresist layer to the top surface of mandrel layer, exposing the
photoresist layer to actinic radiation through a photomask having a
pattern of islands 110A and 110B and then developing the exposed
photoresist layer to form islands 110A and 110B.
[0012] Photoresist resist islands 110A and 110B have a width W1 and
are spaced apart a distance W1 (through section 1A-1A). W1 is the
minimum dimension of a line/space printable by the photolithography
process (described supra) used to form photoresist regions 110A and
110B. In one example W1 is 60 nm or less.
[0013] In one example, underlying layer 100 comprises a low-K
(dielectric constant) material, examples of which include but are
not limited to hydrogen silsesquioxane polymer (HSQ), methyl
silsesquioxane polymer (MSQ), SiLK.TM. (polyphenylene oligomer)
manufactured by Dow Chemical, Midland, Tex., Black Diamond.TM.
(methyl doped silica or SiO.sub.x(CH.sub.3).sub.y or
SiC.sub.xO.sub.yH.sub.y or SiOCH) manufactured by Applied
Materials, Santa Clara, Calif., organosilicate glass (SiCOH), and
porous SiCOH. A low-K dielectric material has a relative
permittivity of about 2.7 or less. In one example, underlying layer
100 comprises silicon dioxide (SiO.sub.2), silicon nitride
(Si.sub.3N.sub.4), silicon carbide (SiC), silicon oxy nitride
(SiON), silicon oxy carbide (SiOC), organosilicate glass (SiCOH),
plasma-enhanced silicon nitride (PSiN.sub.x) or NBLok (SiC(N,H)).
In one example, underlying layer 100 is about 100 nm to about 200
nm thick.
[0014] In one example, mandrel layer 105 comprises amorphous
silicon. In one example, mandrel layer 105 is about 50 nm to about
200 nm thick.
[0015] In FIGS. 2A and 2B, photoresist regions 110A and 110B (see
FIGS. 1A and 1B) are optionally trimmed to form respective trimmed
photoresist regions 115A and 115B. In one example, trimming is
accomplished by a plasma etch process, for example, an oxygen-based
plasma etch. Trimmed photoresist resist islands 115A and 115B have
a width W2 and are spaced apart a distance W3 (through section
2A-2A), where advantageously W2 equals W1 divided by two and W3 is
thrice W2. However, W2 can have any greater than zero and value
less than W1 with W3 increasing by the absolute difference between
W1 and W2. One advantage of performing trimming is to pack the
features subsequently formed and described infra more closely,
allowing equal sub-lithographic dimensions between more of the
features.
[0016] In FIGS. 3A and 3B, the pattern of trimmed photoresist
regions 115A and 115B (see FIGS. 2A and 2B) is transferred into
mandrel layer 105 (see FIG. 2B) by etching (for example, using a
reactive ion etch (RIE) process) away all of the mandrel layer not
protected by the photoresist regions. Then the trimmed photoresist
regions are removed leaving respective mandrels 120A and 120B
having widths of about W2 and spaced apart about a distance W3.
[0017] In FIGS. 4A and 4B, spacers 125 are formed on the sidewalls
of mandrels 120A and 120B. Spacers 125 may be formed by deposition
of a conformal layer, followed by a directional RIE (perpendicular
to the top surface of underlying layer 100) to remove the conformal
layer from all horizontal surfaces (e.g. surfaces parallel to the
top surface of underlying layer 100). In one example, spacers 125
comprises silicon nitride. In one example, spacers 125
advantageously have a sidewall thickness (in the horizontal
direction) of about W2, which makes the space between respective
spacers 125 on opposing sidewalls of mandrels 120A and 120B about
W2. However, the sidewall thickness of spacers 125 may be less than
or greater than W2.
[0018] If photoresist regions 110A and 10B (see FIGS. 1A and 1B)
were not trimmed as illustrated in FIGS. 2A and 2B and describes
supra, spacers 125 may still have a width W2, but the space between
adjacent spacers 125 need not be W2, the space could be greater or
less than W2. However, W2 is still a sub-lithographic
dimension.
[0019] In FIGS. 5A and 5B, mandrels 120A and 120B (see FIGS, 4A and
4B) are removed, for example by wet or dry etching, leaving spacers
125. After removing mandrels 120A and 120B, spacers 125 form a
pattern defined by the sidewalls of the mandrels.
[0020] In FIGS. 6A and 6B, second spacers 130 are formed on the
sidewalls of spacers 125. Between adjacent spacers 125, spacers 130
overlap so as to fully cover underlying layer 100. In one example,
spacers 130 advantageously have a sidewall thickness (in the
horizontal direction) of about 0.9 times W1. In one example,
spacers 130 comprise amorphous silicon. The sidewall thickness of
spacers 130 should be great enough to allow landing of the edge of
a block mask as illustrated in FIGS. 8A, 8B and 8C and described
infra.
[0021] In FIGS. 7A and 7B, spacers 125 (see FIGS. 6A and 6B) are
removed, for example, by wet or dry etching, leaving spacers 130.
After removing spacers 125, spacers 130 form a pattern that in
dense pattern regions is the reverse of the pattern formed by
spacers 125. In dense pattern regions the pattern formed by spacers
130 is a reverse of the pattern formed by spacers 125 because all
regions of underlying layer 100 that were not covered by spacers
125 are covered by spacers 130 and all regions of underlying layer
100 that were covered by spacers 125 are not covered by spacers
130. Dense pattern regions are defined as those regions where
spacers 125 are sufficiently close together that spacers 130
completely cover underlying layer 100 between adjacent spacers 125.
Alternatively, dense pattern regions can be defined as regions
where the distance between adjacent spacers 125 is no more than
about twice the thickness of spacers 130 on the sidewalls of
spacers 125.
[0022] In FIGS. 8A, 8B and 8C, a second photolithographic process
is performed, forming photoresist regions 135. In the illustrated
example photoresist regions 135 overlap the outermost edges of
spacers 130 and cover selected regions of underlying layer 100
outside of the outermost spacers 130. Regions 150 (see FIG. 9A) of
underlying layer 100 are also exposed where edges of photoresist
regions 135 are landed directly on the top surface of the
underlying layer. Regions 150 have a width W4 (in the direction of
section line 8B-8B). W4 is greater than W2. In one example, W4 is
at least equal to or greater than W1. In one example, W4 is equal
to or greater than the minimum dimension of a line/space printable
by the photolithography process used to form photoresist regions
135 or photoresist regions I 10A and I 10B (see FIGS. 1A and 1B).
Photoresist regions 135 also cover portions of underlying layer 100
inside of the outermost spacers 130, where the closed-loop topology
of spacers 130 would otherwise and undesirably lead to continuous
loops of exposed underlying layer 100. The dashed lines of FIG. 8A
show the spacer 130 where it extends under photoresist regions
135.
[0023] In FIGS. 9A, 9B and 9C, spacers 130 and photoresist regions
135 are used as an etch mask to form trenches 145 and 150 into
underlying layer 100. In one example, trenches 145 and 150 are
formed by RIE. Trenches 145 have a width about equal to W2 and
trench 150 has a width about equal to W4 (in the direction of
section line 9B-9B). The dashed lines of FIG. 9A show the spacer
130 where it extends under photoresist regions 135.
[0024] In FIGS. 10A and 10B, photoresist regions 135 and spacers
130 (see FIGS. 9A, (B and 9C) are removed, by wet or dry etching,
leaving trenches 145 and 150 in underlying layer 100. Since
trenches 145 have a width W2 which is smaller than a minimum
photolithographic dimension and trenches 150 have a width W4 which
is equal to or greater than a minimum photolithographic dimension,
both lithographic and sub-lithographic dimensioned structures have
been formed simultaneously using only two photolithographic steps.
It should be noted that photoresist regions 135 (see FIG. 9A) have
prevented interconnection of adjacent trenches 145 by preventing
etching of underlying layer 100 between spacers 130 where the
islands fill the spaces between spacers 130 (see the dashed lines
of FIGS. 8A and 9A).
[0025] FIG. 11A is a top view and FIG. 11B is a cross-sectional
view through line 11B-11B of FIG. 11A illustrating a further step
in the fabrication of a structure according to embodiments of the
present invention. In FIGS. 11A and 11B, trenches 145 and 150 (see
FIGS. 10A and 10B) are filled with a electrical conductor to form
respective wires 155 and 160. In one example, wires 155 and 160
comprise copper, tungsten, tantalum, tantalum nitride, titanium,
titanium nitride, aluminum or combinations thereof and are formed
by plating a layer of copper on underlying layer 100 that is
thicker than trenches to be filled and then performing a chemical
mechanical polish, removing excess copper in order to coplanarize
top surfaces of wires 155 and 160 with the top surface of
underlying layer 100. Wires 155 and 160 are damascene wires. Wires
155 and 160 may include an electrically conductive liner on the
sidewalls and bottom surface of the wires.
[0026] Thus, the embodiments of the present invention provide a
method for forming structures having lithographic and
sub-lithographic dimensions.
[0027] The description of the embodiments of the present invention
is given above for the understanding of the present invention. It
will be understood that the invention is not limited to the
particular embodiments described herein, but is capable of various
modifications, rearrangements and substitutions as will now become
apparent to those skilled in the art without departing from the
scope of the invention. Therefore, it is intended that the
following claims cover all such modifications and changes as fall
within the true spirit and scope of the invention.
* * * * *